Radio transmission system



lJurne 1, 1937. G. H. BROWN 2,082,096

RADIO TRANSMISS ION SYSTEM ATTORNEY June l, 1937.

G. H, BROWN v RADIO TRANSMISSION SYSTEM 2 Sheets-Sheet 2 Filed Nov. 19, 1935 t ob Q g M INVEN'OR George H. .Brown w www tosmuuw toswgt Patented June l, 1937 t v l UNITED STATES PATENT OFFICE aosaoso RADIO TRANSMISSION SYSTEM George H. Brown, Haddoniielrl, VN. J., assigner to Radio Corporation of America, a corporation of Delaware Application November 19, 1935, Serial No. 50,500*

8 Claims. (Cl. Z50-9) My invention relates broadly to a radio transcharacteristic of a suitable filter such as may be mission system. More specically my invention employed in my inVentiOn. relates to a transmission system in which a, .'zIn Figure 1 a pair of radiotransmittersare single antenna structure is connected to two represented by block diagrams l, 3, and l, 9, il', 5 radio frequency generators operating at dif- These transmitters arecomprised of oscillators; ferent frequencies. My invention further relates modulators, and ampliflerS- Since each 0f these to the radiation of radio frequency energy on units are not part 0f my invention. per se, and different wave lengths and with different field are well known to those skilled in the art, I have patterns. i not attempted to illustrate the details of each. 10' An ecient radio broadcast station usually em- Eech o the Stations are generating radio frel0 ploys an antenna structure which will give maxquency carrier currents 0f adiiferent frequencyirnum transmission range for the applied power. Tl'leSe carrier currentS may be modulated by tele- Such antenna structures are relatively expensive Phonic Signals, or the like, 0f the Same 0r differat the lower broadcast frequencies. Ii two or ent criein- The modulated carrier currents may more broadcasting stations could operate at difbe amplified- The outputs of the ampliers 5, l5 ferent frequencies with a common antenna,V a il muy include resonantV circuits |3|5 vThe great saving would result. The common antenna resonant Output circuits |35 are coupled reof my invention not only effects a saving but SDectiVelY to a Pair Of concentric conductors it avoids the distortion of fieid pattern and modl1-l9 through a pair 0f Suitable matching ciruiation which often occurs when two transmitcuits `2i-2i- The output ends of leach of the ting antennas are operated relatively close to concentric linee terminate in matching imped- 20 each other in space and in frequency In many ances comprising inductors 25, 21gand-capacitors cases each transmitter or station will beoper- 29, 3l The concentric linee and their termiated with a different field pattern. 1: propose Hating impedances areerounded.

.25 to combine the antenna structure and at the .T the frequency of one Oscillator l iS f1 and 25 same time preserve any desired directional transthe frequency of the Other Oscillator 'l iS f 2, IneanS mission or field pattern which could be obtained must be employed to couple each Oscillator to with the common antenna structure when Opta common antenna 33 and to prevent coupling grated byseparate transmitters, between the two oscillators throughV their asso'- one 0f the Objects of my invention is to use ciated circuits. Such means is found'in'the filter r a, common antenna, Structure fnr the transmisnetworks 35, 31. The filter network -connected sion of two or more radio programs on diierbetween the antenna 33 and the terminating iment Wave 1eng1-,hs or frequencies., pedance 25-29 is series resonant to currents of Another object is to radiate,` from a single frequency f1 from the first oscillatcr l. The antenna system, two or more radio frequency Parallel impedance Of the lilter 35 is a maximum 35 waves at 'different wavelengths and with diierfor currents 0f frequency f2 from second oscilent eld patternn n l lator 1. Thus the lter network 35 offers min- A further Object is to arrange la transmission irnurn impedance to currents cwing from the network between a single antenna system and firet'treneinitter l, 3, 5 'and maximum impedance 40 two or `more transmitters operating on different t0 currents from theeecond transmitter l, 9, li- 40 frequencies so that the transmitters will `not In e Similar manner" the filter 31 is series intermodula. Y resonant to currentsof a frequency f2 from the Additional objects will appear from the M second oscillator 'l and parallel resonant to curu rents of a frequency fi from the first Oscillator I. compapymg .Speclcatlon and appended Cla'mts Thus this filter network oifers very little imped- My 1nvention may be most readily understood ance to currents owin from th d t 45 by reference to the accompanying drawings of g e secon mns' p. mitter 1, S, Il and maximum impedance to curwh1ch Figure 1 is a diagrammatic illustration of rents from the rst transmitter I 3, 5. one embodiment of myinvention,

Although filter networks of numerous types 5 Flgure 2 1S a Scheinen? diagram of en embodlmay he used, I have found that if f1 is of higher 50 ment of my 1nvention m Winch a' pau' of an' frequency than f2, a network 35 comprising two tennas are used as common radiators and in arms may be use@ one 0f these arms employs which the radiation patterns may be diirerent, an inductor 39 and a capacitor 4|. The other and arm is an inductor 43 which shunts the first arm.

Figure 3 is a graph showing the impedance The first arm of inductor 39 and capacitor 4| is 55 series resonant to currents of the higher frequency f1. The two arms comprising inductor 39, capacitor 4I, and inductor 43 are parallel resonant; to currents of the lower frequency.

As a similar example the filter network 31 is made up of two arms. One of the arms consists of inductor 45 and a capacitor 41. The other arm is a capacitor49 which is shunted across the first arm. The inductor 45 and capacitor 41 are series resonant to currents of the lower frequency f2. The two arms comprising inductor 45, capacitor 41 and capacitor 49 are parallel resonant to currents of the higher frequency f1.

By way of example, if f1r=1290 kilocycles and f2=920 kilocycles, the lterfnetwork 35 may be constituted as follows:

C1=257 10-12 farads R1=Resistance of coil L1=1.15 ohms R2: do. y L2=1.15 do.

In this combination, L1C1 constitute one arm and Lz is the other armof the lter network. Figure 3 is a graph representing the impedance of thislter in yohms plotted against frequency in kilocycles. It may be seen that the impedance to currents of the higher frequency f1 is 1.1 ohms. The impedance to currents of the lower frequency` f2 is 54,000 ohms.

A similar result may be obtained for the net- Work representedV as-31. vIf the two transmitters are operating on greatly different powers, a single filter network may offer sufficient attenuation to prevent undesirable modulation effects.

The foregoing embodiment of my invention is applicable to a common antenna structure associated with a pair of transmitters or generators operating at different frequencies. In Figure 2 I have illustrated an embodiment of my invention in which a pair of antenna structures are made common radiators fora pair of generators operating at different frequencies. In this arrange ment the essential' difference is that the relative phases ofthe currents of leach frequency may be separately adjusted in each antenna. By properly phasing the respective currents, the `same or different eld patterns may be obtained for the different frequencies. l

The field pattern determines the directive characteristic of the transmitters. The directive characteristic of two or more antennas is not, per se, my invention. The :design of suchy antenna arrays is discussed fully'in a paper entitled Certain factors affecting the gain of directive antennas by G. C. Southworth in the Proceedings o-f the Institute of Radio Engineers for September, 1930 (vol. 18, No. 9, pages 1502-1536). As a practical matter it is often highly desirable to suppress the radiation of a wave of one frequency in a given direction and toi-suppress the wave of another frequencyk in some other direction.- In like manner it may be desirable to increase radiation in a given direction;

'Ihe circuit diagram shown in Figure 2 is essentially the same as Figure 1; therefore, similar elements are given similar reference numerals. The present diagram indicates a pair of transmitters I, 3, 5 and 1, 9, II. Each transmitter impresses modulated carrier currents on pairs of concentric transmission lines I1, I1 and I9, I9. The terminals of the transmission lines are each connected to suitable impedance circuits 25, 29 and 21, 3I. Filter `networks,f35, 35 and 31, 31 are connected between the terminations of the concentric lines and the antennas 33, 33. The filter networks operate to offer low series impedance to currents from each transmitter to the antennas but high parallel impedance to currents between the transmitters themselves.

The desired eld pattern is obtained by including a phasing network 5I, 53 in one of each of the pairs of concentric transmission lines from each of the transmitters. The phasing network 5I operates to alter the relative phases of currents of frequencies f1, in the pair of antennas to which the transmitter I, 3, 5 is coupled. In like matter the reactor 53 operates to alter the relative phases of currents of frequency f2 in the pair of antennas to which the transmitter 1, 9, I I is coupled. Since the filter networks 35, 31 substantially prevent the reaction of currents from the two transmitters, it is entirely feasible to adjust the phases of antenna currents of one frequency independent of antenna currents of the other frequency.

Thus I have described an antenna system'in which a common radiator or antenna structure may be used for two or more transmitters operating on different frequencies. The circuit arrangements are adapted to the use of two or moreA antennas and two or more transmitters operating at dierent frequencies and having different field patterns. In the case of a dipole antenna, pairs of iilter networks may be used. Although I have shown concentric lines, I do not intend to exclude the use of transposed transmission lines, and the like. The illustration of pairs of antennas and pairs of transmitters is merely by way of example, because a plurality of either may be used.

While I have shown one type of filter network, other types will provide satisfactory operation. Two vor more lters may be serially connected to increase attenuation of undesired currents.` My invention is only limited as required by the prior art and the appended claims.

I claim as my invention: i

1. A radio transmission system comprising an antenna; a first transmitter operating at a given frequency; a second transmitter operating at a different frequency from the rst-mentioned frequency; coupling means for couplings said first transmitter to said antenna including a lter composed of three elements, two of which are serially connected and are shunted by the third, said lter being series resonant to currents of the first-mentioned frequency and parallel reso. nant to currents of the second-mentioned` frequency; and means coupling the other of said transmitters to said antenna.

2. A radio transmission system comprising an antenna; a rst transmitter operating at a given frequency; a second transmitter operating at a different frequency froml the first-mentioned frequency; coupling means for coupling said first transmitter to said antenna including a filter composed of three elements, two of which are serially connected and are shunted by the third, said filter being series resonant to currents of the first-mentioned frequency and parallel resonant to currents of the second-mentioned frequency; and a second coupling means for coupling said second transmitter to said antenna including a second lter composed of three elements, two of which are serially connected and are shunted by the third, said second filter being series resonant to currents of the second-mentioned frequency and parallel resonant to currents of the-firstmentioned frequency. y

3. In a system of the class described an antenna; a first generator of currents of frequency f1; a second generator o-f currents of frequency fz; a pair of filter networks, the first of said filters comprising three elements, two of which are serially connected and shunted by a third, said filter being series resonant to currents of f1 frequency and parallel resonant to currents of f2 frequency, the second of said filters comprising three elements, two of which are serially connected and shunted by a third, said second filter being series resonant to currents of f2 frequency and parallel resonant to currents of f1 frequency; means connecting said filters to said antenna; and two concentric lines, one coupling the first filter to the generator of currents of f1 frequency and the other coupling the second filter to the generator of currents of fz frequency.

4. In a radio transmission system, a pair of radio frequency transmitters operating at different frequencies, a plurality of` antenna structures; means coupling the rst of said generators to said antenna structures and comprising three elements, two of which are serially connected and shunted by a third, said lter being series resonant to currents of the frequency of said rst generator and parallel resonant to currents of the frequency of the second of said generators; means coupling the second of said generators to said antenna structures, and phasing means included in the coupling means to at least one of said antenna structures so that the relative phase of currents in said antennas may be adjusted.

5. A radio transmission system comprising a plurality of antennas; a rst transmitter operat-A ing at a given frequency; a second transmitter operating at a different frequency from the rstmentioned frequency; coupling means for coupling said first transmitter to said antennas including a filter comprising a pair of inductors and a capacitor, one of said inductors and said capacitor being serially connected and shunted by the other inductor, said filter being series resonant to currents of the first-mentioned frequency and parallel resonant to currents of the second-mentioned frequency; means coupling the second of said transmitters to said antennas; and means for determining the relative phases of currents of one of said frequencies in said plurality of antennas.

6. In a system of the class described, a plurality of antennas; a first generator of currents of frequency f1; a second generator of currents of frequency f2; a pair of filter networks, the rst of said filters comprising a pair of inductors and a capacitor, oneof said inductors and said capacitor being serially connected and shunted by the other inductor, said first lter being series resonant to currents of f1 frequency and parallel resonant to currents of f2 frequency, the second of said filters comprising a pair of capacitors and an inductor, one of said capacitors and said inductor being serially connected and shunted by the other capacitor, said second filter being series resonant to currents of f2 frequency and parallel resonant to currents of f1 frequency; means connecting said filters to said antennas; two concentric lines, one coupling the rst filter to the generator of currents of f1 frequency and the other coupling the second filter to the generator of currents of f2 frequency; and means for adjusting the relative phases of currents of frequency f1 in different antennas of said plurality of antennas.

7. In a system of the character of claim 5,v

means for determining the relative phases of currents of the other of said frequencies in said plurality of antennas.

8. In a system of the character of claim 6, means for adjusting the relative phases of currents of frequency f2 in different antennas of said plurality of antennas.

GEORGE H. BROWN. 

